We are turning a 127mm part in a double headed center drive lathe. The part sticks out of the chucks about 500mm. The part is first bored and then supported by a tailstock. The OD tolerance is +/- 0.019mm. The CPk for this process is not acceptable. When we run 25 parts 22-23 are excellant and within tolerance. If these were the only parts the process would have an acceptable CPk. The problem is the other 2-3 parts. They are flyers and are both over or under tolerance by 0.1mm or more. Can anyone help with a list to things to check to find the source of the variation? I am leaving off the list of items we already checked so as to not limit the ideas you many have.